Apparatus and method for removing solvent from carbon dioxide in resin recycling system

ABSTRACT

A two-step resin recycling system and method solvent that produces essentially contaminant-free synthetic resin material. The system and method includes one or more solvent wash vessels to expose resin particles to a solvent, the solvent contacting the resin particles in the one or more solvent wash vessels to substantially remove contaminants on the resin particles. A separator is provided to separate the solvent from the resin particles after removal from the one or more solvent wash vessels. The resin particles are next exposed to carbon dioxide in a closed loop carbon dioxide system. The closed loop system includes a carbon dioxide vessel where the carbon dioxide is exposed to the resin, substantially removing any residual solvent remaining on the resin particles after separation. A separation vessel is also provided to separate the solvent from the solvent laden carbon dioxide. Both the carbon dioxide and the solvent are reused after separation in the separation vessel.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part (CIP) of U.S. patentapplication Ser. No. 11/096,880, filed Apr. 1, 2005, U.S. patentapplication Ser. No. 11/426,530 filed Jun. 26, 2006, U.S. applicationSer. No. 11/426,522 filed Jun. 26, 2006, and U.S. application Ser. No.11/426,503 filed Jun. 26, 2006, all of which are incorporated byreference herein for all purposes.

GOVERNMENT SPONSORED DEVELOPMENT

The U.S. Government has rights in this invention pursuant to contractnumber DE-ACO4-01AL66850 with the United States Department of Energy.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an improved system for removingcontaminants from synthetic resin materials, such as plastic. Moreparticularly, the present invention relates a resin recycling systemthat produces essentially contaminant-free synthetic resin material inan environmentally safe and economical manner.

2. Description of the Prior Art

Recycling containers made from synthetic resin material is a highlydesirable alternative to landfilling such containers. However, thesecontainers often include residues of the material they once contained.These residues if not removed can decrease the value of the containermaterial making it suitable for only low-grade products. Traditionally,these residues or contaminants have been difficult and expensive toremove and prone to create additional waste byproducts.

Recycling of motor oil containers is illustrative of the problem. Motoroil containers typically are high-density polyethylene (HDPE) whichlends itself well to recycling if it is sufficiently clean. However,residual oil coating the interior surface of the “empty” motor oilcontainers constitutes a contaminant that prevents re-use of thecontainers in at least a high grade plastic application, such as thepackaging of food or beverages.

The aforementioned problem is not just limited to oil containers.Similar contamination problems exist for example with pesticides fromHDPE containers, milk from HDPE containers, “soda water” frompolyethylene terephthalate (PET) containers, polychlorinated biphenyl(PCB) contaminants particularly from automotive plastics, andcontaminants from various other post-consumer containers, such asdetergent containers, collected from curbside recycling programs.

The significant amount of the above mentioned types of containers arecurrently disposed of in landfills, leaking oil and other contaminantsinto the soil and groundwater, and occupying significant landfillvolume.

Several known options exist other than landfilling the waste syntheticresin containers, including (a) grinding the containers and using themin other recycling processes on a very limited (dilute) basis; (b) usingan aqueous process to displace the contaminant from the synthetic resinmaterial; (c) using a halogenated solvent to dissolve/dilute thecontaminant; or (d) using a combustible or flammable solvent todissolve/dilute the contaminant oil from the synthetic resin material.

The problems with these options are as follows:

Existing recyclers in the United States can blend limited quantities ofcontaminated synthetic resin materials in recycled products. Largequantities cannot be blended because of the undesirable effects of thecontaminants on the recycled synthetic resin material properties.Examples include “plastic lumber” and lower grade plastic products.

Aqueous processes can be used to displace the contaminants from thesynthetic resin material. However, detergents and/or surfactants arerequired to assist displacement of the contaminants. A stream of usablecontaminant-free synthetic resin material will be generated by thismethod; however, the displaced contaminants will need additionalprocessing to separate them from the aqueous solutions or dispersions.The aqueous solutions or dispersions themselves will be a secondarywaste stream that will require treatment before being recycled ordischarged as waste water.

Halogenated solvents can be used to dissolve/dilute the contaminantsfrom the synthetic resin material. Again, usable synthetic resinmaterial will be obtained by this process if the solvents do not extractessential components from the synthetic resin material. The halogenatedsolvent solutions will require distillation to recover the contaminantsand recycle the solvents. In general, it is difficult to fully reclaimusable contaminants (such as oil) from the distillate. Furthermore, manyhalogenated solvents are ozone depleting compounds and potential healthhazards to humans, and therefore their use and release into theenvironment are under regulation and close scrutiny by federal and stategovernments.

Combustible or flammable solvents may be used to dissolve and/ordisplace the contaminants from the synthetic resin material. Usablesynthetic resin material can be generated by this method if the solventsdo not extract essential components from the synthetic resin material.The combustible or flammable solvent solutions will require distillationto recover the contaminants and recycle the solvents. Only distillationequipment suitable for combustible or flammable solvents may be used andeven then fire safety concerns will be significant. As in the case ofthe use of halogenated solvents, the contaminant may not be fullyrecoverable from the distillation.

Accordingly, there is a need for a system and method that will produceessentially contaminant-free synthetic resin material in anenvironmentally safe and economical manner and further including asolvent cleaning system for periodically removing the contaminants fromthe solvent used to remove the contaminants from the resin so that thesolvent can be reused and the contaminants can be collected and safelydiscarded in an environmentally safe manner.

SUMMARY OF THE INVENTION

The present invention solves the above-described problems and isdirected to a two step solvent and carbon dioxide based system thatproduces essentially contaminant-free synthetic resin material. Thesystem and method includes one or more solvent wash vessels to exposeresin particles to a solvent, the solvent contacting the resin particlesin the one or more solvent wash vessels to substantially removecontaminants on the resin particles. A separator is provided to separatethe solvent from the resin particles after removal from the one or moresolvent wash vessels. The resin particles are next exposed to carbondioxide in a closed loop carbon dioxide system. The closed loop systemincludes a carbon dioxide vessel where the carbon dioxide is exposed tothe resin, substantially removing any residual solvent remaining on theresin particles after separation. A separation vessel is also providedto separate the solvent from the solvent laden carbon dioxide. Both thecarbon dioxide and the solvent are reused after separation in theseparation vessel.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

A preferred embodiment of the present invention is described in detailbelow with reference to the attached drawing figures, wherein:

FIG. 1 is a schematic flow diagram depicting a three-stage solventsystem and a liquid or supercritical carbon dioxide system for removingcontaminants from particulate synthetic resin material.

FIG. 2 is a detailed view of the three-stage solvent system shown inFIG. 1.

FIG. 3 is a diagram illustrating a resin recycling method and apparatusaccording to the present invention.

Like reference numbers in the figures refer to like elements.

The drawing figures do not limit the present invention to the specificembodiments disclosed and described herein. The drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to the drawing figures, and particularly FIG. 1, a processfor removing contaminants from post-consumer containers made fromsynthetic resin material in accordance with a preferred embodiment ofthe invention is illustrated. The present invention is particularlyuseful in the removal of oil from high-density polyethylene containers,pesticides from HDPE containers, milk from HDPE containers, “soda water”from polyethylene terephthalate containers, polychlorinated biphenyl(PCB) contaminants particularly from automotive plastics, andcontaminants from various other post-consumer containers, such asdetergent containers, collected from curbside recycling programs. Also,the present system is highly effective in removing labels and labeladhesive from synthetic resin material containers. Furthermore, thepresent invention facilitates contaminant recovery from synthetic resinmaterials thereby enabling the contaminants to be disposed of in a safeand environmentally friendly manner.

The upstream portion of the process comprises a liquid solvent cleaningsystem 10. Solvent cleaning system generally includes three separatecleaning stages 12, 14, and 16. Particulate synthetic resin material(illustrated as feed stream 18) is initially loaded into the first stage12, which contains a liquid solvent. After a first cleaning cycle duringwhich the particulate material is vigorously mixed with the solvent, theparticulate material (illustrated as stream 20) is transferred to asecond stage 14. Stage 14 operates in a very similar manner to stage 12in that the particulate material is mixed with additional quantities ofsolvent. After the second cleaning cycle, the particulate material(illustrated as stream 22) is transferred to a third cleaning stage 16.The third stage 16 also is similar in operation to the first two stages12, 14. However, for reasons explained in greater detail below, thisstage preferably employs a greater quantity of solvent than either ofthe first two stages. Also, the solvent purity preferably increases fromstage 12 to stage 14 to stage 16. The solvent contained in eachsuccessive stage is preferably cleaner than the previous stage in orderto achieve the maximum solvation of the contaminants present on thesynthetic resin material.

It will be appreciated that the stages 12, 14, and 16 do not necessarilyneed to be carried out in separate vessels. It is believed that theoverall process functions most efficiently when these stages are carriedout in separate vessels arranged in series, as a nearly continuousprocess can be achieved. However, it is possible that fewer than threeseparate vessels could be used and instead of the resin material beingtransferred from tank to tank, different batches of solvent (havingdifferent purities) may be moved in and out of the tank during eachstage. In such manner, the particulate synthetic resin material is stillcontacted by three different batches of solvent, but need not leave theconfines of a single vessel.

The particulate material (illustrated as stream 24) is then sent to asolvent separation and recycle station 26. At station 26, a substantialportion of the solvent is separated from the particulate material andrecycled to the third cleaning stage 16 via conduit 28. Station 26preferably employs a device, such as a spin dryer, to mechanicallyseparate the solvent from the particulate material. The particulatematerial is then sent to a silo 30 via stream 32 to await furtherprocessing.

The downstream portion of the process comprises a carbon dioxidecleaning system 34. The setup of system 34 is nearly the same as thatdisclosed in U.S. Pat. No. 5,711,820, which is incorporated by referenceherein. The objective of carbon dioxide system 34 in the context of thepresent invention is slightly different than in the '820 patent. In thepresent process, a substantial portion, and preferably almost all, ofthe contaminants are removed from the synthetic resin material prior toreaching carbon dioxide system 34. However, what remains on thesynthetic resin material, in addition to trace amounts of contaminants,is mainly solvent from solvent cleaning system 10. At this stage, thesynthetic resin flakes may still comprise between 0.1-5% by weightsolvent which must be removed. Carbon dioxide system 34 is used toremove this solvent that is left over from solvent cleaning system 10.Unlike the process shown in the '820 patent, the present carbon dioxidesystem 34 is not principally directed toward removing oil contaminantsfrom the synthetic resin flakes, but instead is directed toward removingresidual solvent from the earlier system. Small amounts of contaminantsmay still be removed from the flakes during operation of carbon dioxidesystem 34, however, this is an incidental benefit as the vast majorityof the contaminants have already been removed during the solventcleaning system 10.

Preferably, the solvent used in solvent cleaning system 10 is relativelysoluble in liquid or supercritical carbon dioxide (more so than thecontaminants being removed from the synthetic resin material in system10). Therefore, one advantage of the present system is that carbondioxide system 34 can operate at lower pressures than if carbon dioxidesystem 34 were directly solvating the contaminants. Operation at lowerpressures tremendously lowers equipment costs and energy costsassociated with liquefying the carbon dioxide.

As indicated by the dashed line, system 10 is preferably a closed systememploying vessels that are sealed or blanketed with an inert gas such asnitrogen to prevent volatilization and escape of solvent to the outsideenvironment. In addition, silo 30 is preferably a closed vessel and doesnot permit much if any residual solvent adhered to the synthetic resinparticles to escape to the environment. As a closed system, system 10does not present significant environmental concerns as it is relativelyself-contained and does not produce significant emissions. Also, theclosed nature of system 10 allows for recycling of a substantial portionof the liquid solvent used therein with low make up demands. Thesefeatures result in a reduction in operating costs of approximately 40%compared to conventional water-based contaminant removal systems andalso avoids having to deal with the clean up of contaminated water.

Turning now to FIG. 2, the solvent cleaning system 10 is shown ingreater detail. Stages 12, 14 and 16 are relatively similar with thepossible exception of equipment sizing. Therefore, those features commonto all three stages are described using the same reference numerals. Afeed stream 18 of particulate material ground into approximately ⅜″flakes enters stage 12 and is directed initially to a separator 36primarily for separation of unacceptably large particles of syntheticresin material that could be difficult to process. The separator can beany sieve or filter-type apparatus suitable for performing thisseparation, however, apparatus such as a Sweco separator is preferred.The rejected particles exit separator 36 through stream 38 and may bereturned to a shredding or grinding device (not shown) for furtherprocessing to reach an acceptable size (approximately ⅜″).

Synthetic resin particles of acceptable size exit separator 36 throughstream 40 and are directed toward a conveyer 42 for distribution toeither of cleaning tanks 44 or 46. Conveyer 42 comprises a reversibleauger 48 that is capable of directing the particulate synthetic resinmaterial to both tanks 44 and 46. In operation, material is loaded intoone tank until its capacity has been reached. The cleaning cycle isbegun in that tank and auger 48 reverses direction so as to beginfilling the other tank. By providing two tanks in parallel, a nearlycontinuous process may be achieved.

Tanks 44 and 46 (and all such related tanks) are preferablydouble-walled tanks, the inner compartments 49 of which contain a liquidsolvent capable of dissolving contaminants that may be present on thesynthetic resin material. This double-wall feature provides extraprotection against accidental release of solvent and contaminants.

A feature unique to tanks 44 and 46 is that these tanks are equipped forseparation of less dense synthetic resin material from more densematerial. For example, many synthetic resin material containers madefrom polyethylene terephthalate (PET) employ caps made from less densepolypropylene material. It is often desirable to separate these twokinds of materials during recycling operations. Manual separation ofthese different materials can be very costly. The present inventionaccomplishes this separation through the careful selection of a solventthat has a specific gravity in between the specific gravities of the twokinds of materials. Therefore, the less dense polypropylene materialwill float in the solvent while the denser PET tends to sink. A skimmingdevice may be used to remove the lesser dense material from tanks 44 and46 via streams 52 and 54, respectively. Alternatively, gates locatedproximate the top of tanks 44 and 46 open thereby draining the lesserdense material along with a quantity of solvent which is then filteredand the solvent returned to the respective tank. In some instances, thedesired synthetic resin material may have a density that is too close tothat of the cap material to facilitate floatation separation. It is thendesirable to separate the caps from the containers prior to grinding ofthe containers.

Each of tanks 44 and 46 is equipped with a mixer 50 for agitating thecontents of the tank. Preferably, this agitation is quite significantand can be characterized as violent so as to insure the maximum possiblecontact of the synthetic resin material with the solvent. A preferredmixer 50 for use with the present system is a Neptune mixer having atleast one propeller attached to the mixer shaft.

As previously stated, tanks 44 and 46 are jacketed. The outercompartment 56 of each tank contains a heat transfer fluid for heatingand maintaining the temperature of the solvent within the innercompartment 49. Preferably, any suitable heat transfer fluid may beused, however, a glycol such as propylene glycol or ethylene glycol isparticularly preferred. The heat transfer fluid is preferably heated toa temperature of between about 170-190° F. using heat exchanger 58.Consequently, the solvent contained within the inner compartment 49 willalso be heated to a temperature between about 170-190° F. Using ajacketed vessel to heat the solvent allows heating to be accomplishedwithout use of an open flame near the solvent vessel. This feature addsto the overall safety of the system. The glycol solution is constantlycirculated between tanks 44 and 46 and heat exchanger 50 via conduits60, 62, 64, and 68.

In alternative embodiments, the solvent is not heated to such a hightemperature. For example, the solvent can be heated in the range of 90to 110° F. In one specific embodiment, the solvent is heated toapproximately 100° F. The lower temperatures help reduce operating costsand reduce the amount of solvent loss due to evaporation.

The synthetic resin particles and solvent are agitated for apredetermined length of time. This length of time is dependant upon manyfactors such as tank size, solvent purity, and the nature of the solventitself and its capacity for solubilizing the particular contaminants.However, it is preferable for agitation to occur over a relatively shorttime period, preferably less than 15 minutes, more preferably between1-12 minutes, and most preferably between about 4-5 minutes. At the endof the agitation cycle, the contents of either tank 44 or 46 are emptiedvia conduit 70 or 72, respectively. The slurry comprising solvent andsynthetic resin material is then pumped by pump 74 and directed to stage14 via conduit 76.

The slurry passes through a second separator 36 whereby the particulatematerial is separated from the solvent, which is then recycled back tostage 12 via conduit 78. Pump 80 directs the recycled solvent to eithertank 44 or 46 via conduits 82 or 84, respectively. The synthetic resinmaterial (illustrated as stream 86) is directed to a second conveyer 42,which distributes the particulate material between tanks 44 b and 46 b.Stage 14 then operates in a similar manner to stage 12 with theexception of the extra step of separating synthetic resin materials ofdifferent densities by flotation removal.

At the completion of the agitation cycle, the slurry of solvent andparticulate material exits the respective tank through conduit 88 or 90and is pumped by pump 92 to stage 16 via conduit 94. Stage 16 beginswith the slurry being passed through a third separator 36 with thesolvent being separated and recycled back to stage 14 through conduit96. Pump 98 directs the recycled solvent back to the appropriate tankthrough either conduit 100 or 102.

The synthetic resin material leaves separator 36 as stream 104 and isdirected to conveyer 42 for distribution between tanks 44 c and 46 c.Stage 16 then operates in a manner that is similar to the operation ofstages 12 and 14. At the completion of the agitation cycle, the solventand synthetic resin material slurry exits tanks 44 c and 46 c viaconduits 106 and 108, respectively, and is pumped by pump 110 to hydrocyclone 112 via conduit 114

The hydro cyclone 112 separates solid waste material present in theslurry from the particulate synthetic resin material. The solid wastecould be any undesirable particulate material present in the slurryincluding metal particles and other heavy solid particles thatheretofore may have not been separated from the synthetic resin materialor solvent. This waste then exits the system as stream 116. The ratio ofsolvent to synthetic resin material present in the slurry entering thehydro cyclone is dependent upon a number of factors such as the densityof the synthetic resin material. Furthermore, the interior of the hydrocyclone must be changed out depending upon the different types ofsynthetic resin material present in the slurry.

The slurry is directed through conduit 118 toward spin dryer 120 where asubstantial portion of the solvent is separated from the synthetic resinmaterial and recycled back to stage 16 through conduit 122 and pump 124.The recycled solvent is then distributed between tanks 44 c and 46 cthrough conduits 126 and 128. Spin dryer 120 preferably removes at leastabout 90% by weight of the solvent present in the slurry, morepreferably at least about 95% by weight of the solvent, and mostpreferably at least about 98% by weight of the solvent. After exitingthe spin dryer, the particulate synthetic resin material is transportedas stream 130 to storage silo 30 where it is held until it can be sentto carbon dioxide system 34.

The solvent used in system 10 is carefully selected based on variousdesirable characteristics. First, the solvent should be capable ofsolvating a number of different kinds of contaminants without causingsignificant break down of the synthetic resin materials dispersedtherein. Second, the solvent should exhibit a specific gravity tofacilitate flotation separation of synthetic resin materials ofdifferent densities. Using the polypropylene cap and PET containerexample, it is desirable to separate the cap material from the morevaluable PET. The polypropylene material exhibits a specific gravity ofabout 0.90 whereas PET generally exhibits a specific gravity of betweenabout 1.3-1.4. Preferably, the solvent will have a specific gravity inbetween these two figures and more preferably will have a specificgravity proximate to that of water. If flotation separation is not acritical feature of the particular process, the specific gravity of thesolvent is not as critical a factor. However, it is preferable for thesolvent to comprise an organic solvent other than carbon dioxide havinga specific gravity (preferably at 20° C.) of at least about 0.76, morepreferably between about 0.9-1.5, and most preferably between about0.95-1.25. Suitable solvents may be selected from various classes ofchemicals such as esters, ketones, glycols, glycol ethers, halogenatedsolvents, aromatics, alcohols, aliphatic hydrocarbons, amines, andterpenes. More specifically, the solvent is selected from the groupconsisting of amyl propionate, butyl butyrate, alkyl lactates, ethylhexyl acetate, dibasic esters, methyl soyate, ethyl soyate,cyclohexanone, methyl ethyl ketone, dipropylene glycol, dipropyleneglycol methyl ether, trichloroethylene, xylene, ethanol,tetrahydrofurfuryl alcohol, hexane, mineral spirits, monoethanolamine,d-limonene, dimethyl formamide, n-methyl pyrrolidone, propylenecarbonate, and combinations thereof. Preferably, the solvent is an alkylester solvent having the general formula RCOOR′, wherein R and R′ areindependently selected from C1-C10 alkyl groups and R contains at leastone hydroxyl group. Alkyl lactates are particularly preferred solventsfor use with the present invention.

Preferred alkyl lactates include methyl lactate, ethyl lactate,isopropyl lactate, and butyl lactate, all of which are available underthe name PURASOLV by PURAC America, Inc., Lincolnshire, Ill. Of thealkyl lactates, ethyl lactate is particularly preferred. These solventsexhibit specific gravities at 20° C. of between 0.98-1.09, are generallymiscible with water, and have a high capacity for solvating variousorganic contaminants such as grease and oil. Furthermore, these solventsare relatively non-toxic and, in some instances, have been approved bythe FDA for food applications. The lack of solvent toxicity is an addedbenefit and contributes to the environmentally friendly nature of thissystem.

Solvent compatibility with the synthetic resin material is also animportant property as it is undesirable for the solvent to solvate thesynthetic resin material in addition to the contaminants. Syntheticresin material such as polypropylene, polyethylene, polyethyleneterephthalate, nylon, polytetrafluoroethylene, polytetrafluoroethylene,polyvinylidene fluoride, polycarbonate, fluorinated ethylene propylene,polybutylene terephthalate, polyimide, polyetherketone, polyetherimide,polybutylene, polyphenylene oxide, polystryene, polysulfone,polyethersulfone, polymethylpentene, polyvinyl chloride, acetal,acrylic, acrylonitrile-butadiene-styrene (ABS), and combinationsthereof, are considered to be compatible with many of the preferredsolvents according to the present invention.

Carbon dioxide system 34, as shown in FIG. 1, is an exemplary closedloop separation system suitable for separation of residual solventadhered to the synthetic resin particles after treatment in solventsystem 12. Carbon dioxide system 34 is also capable of removing traceamounts of contaminants that may still be present on the synthetic resinparticles; however, the primary function of system 34 is to separate thesolvent residue from the particles thereby producing solvent andcontaminant free material.

The particulate synthetic resin material is transferred from storagesilo 30 to extraction vessel 132 via stream 134 (preferably an augertransport device). Typically, the material will be enclosed in a steelmesh basket or other porous metal enclosure so that the synthetic resinmaterial will not be swept out of the extraction vessel 132 into otherportions of the separation system 34 by the flowing carbon dioxidedescribed below. The system is then filled with carbon dioxide from areservoir 136 through a control valve 138 to a pressure suitable tosatisfy the desired pressure and temperature conditions in operation asdescribed further below. With the control valves 138 and 140 shut off,carbon dioxide flow is established from the compressor 142 andassociated heat exchanger 144 through control valve 146, through theextraction vessel 132, through the expansion device 148 and associatedheat exchanger 150, through separation vessel 152 and to the compressor142 for another cycle. Adjustments to the compressor 142 speed,expansion device 148, and the temperature of the heat exchangers 144 and150 allows the extraction vessel 132 and separation vessel 152 to bemaintained at the desired pressures and temperatures as describedfurther below. Such adjustments may be made manually or controlled bycommercially-available computer software and equipment. Overall chargeof the system may be adjusted by admitting more carbon dioxide fromreservoir 136 through control valve 138 or by discharging carbon dioxideto the reservoir through control valve 140.

In the extraction vessel 132, the desired temperature and pressure forsolvency of the solvent in liquid or supercritical carbon dioxide istypically from about 600-5000 psia (more preferably from 650-1000 psia,and most preferably from about 700-800 psia) and from about 20-100° C.(more preferably from about 30-90° C., and most preferably from about60-70° C.). The solvent-free liquid or supercritical carbon dioxidecontinuously enters the bottom of the extraction vessel 132 and flowsupward past the synthetic resin material 154, dissolving the solventcarried on the material 154 (from system 10) and flushing it away. It isof some importance that the flow of carbon dioxide be introduced to thebottom of extraction vessel 132, since the upward flow will tend tofluidize the bed of synthetic resin material 154 and hasten dissolutionof the solvent.

The solvent-laden carbon dioxide continuously exits from the top ofextraction vessel 132 and flows to the expansion device 148 and heatexchanger 150. Expansion device 148 and heat exchanger 150 are set suchthat the carbon dioxide entering the separator vessel 152 is in thegaseous phase; typically from about 400-1000 psia and from about 20-35°C. Under these gaseous conditions, the carbon dioxide has negligiblesolubility for the solvent, and therefore the solvent (including anytrace amounts of contaminants) is precipitated out of solution, forminga two-phase system of liquid solvent and gaseous carbon dioxide, and thesolvent collects in the bottom of separator vessel 152. The nowsolvent-free carbon dioxide gas is compressed through the compressor 142wherein the pressure is raised equal to or greater than that of theextraction vessel 132. The temperature of the carbon dioxide then isadjusted to the desired value as it flows through heat exchanger 144,from where it reenters the extraction vessel 132 as either liquid orsupercritical (depending on the pressure and temperature chosen) carbondioxide to again dissolve and flush away solvent from the syntheticresin material 154. This recirculation of the carbon dioxide iscontinued until all of the solvent has been removed from the syntheticresin material and deposited in the separator vessel 152.

When the separation of the solvent from the synthetic resin material iscomplete, with control valve 146 closed, the clean carbon dioxide isrouted into the storage reservoir 136 through control valve 140 to beused again later. The solvent-free synthetic resin material 154 isremoved from the extraction vessel 132 (preferably by a vacuum system)and sent to a storage silo. The solvent 156 recovered is drained fromthe separator vessel 152. The only waste released by this process is thesmall amount of carbon dioxide gas vented during final depressurizationof the extraction vessel 132.

The solvent 156 recovered by carbon dioxide system 34 is preferablyrecycled to solvent cleaning system 10, or if necessary, may be sent toa purification system. Periodically, the solvent used in stages 12, 14,and 16 will need to be changed out and purified as the solvent becomessaturated with contaminants. The time period between these change outsis dependent upon a number of factors including the stage in which thesolvent is being used and the solvents capacity or solvating power(sometime referred to as the Kauri butanol value), but is typicallyevery several hours. The solvent is drained from the respective stageand sent to a distillation system for separation of the solvent and thecontaminants. The operating conditions of the distillation system dependlargely upon the flash point of the solvent, but preferred solventsaccording to the present invention are typically heated to about 300° F.and then re-condensed. The contaminant waste is then properly disposedor recycled. Recovery of the contaminant waste for proper disposal is animportant advantage of the present invention. If the contaminants werenot recovered, particularly the more toxic contaminants, they wouldlikely wind up in a landfill along with the synthetic resin materialwhere they could cause soil and groundwater contamination.

The solvent stages 12, 14, and 16 need not be taken off-line forsubstantial periods of time during this process as fresh solvent can beadded immediately following removal of the “dirty solvent” and theprocess continued while the dirty solvent is being purified. System 10as shown in FIG. 2 is particularly designed to avoid this downtime astanks 44 and 46 are situated in parallel, so that one tank isoperational while the other is taken down for solvent change over. Inessence, the system 10 is designed to function as a continuous-batchprocess.

The aforementioned upstream liquid solvent wash system 10 and downstreamcarbon dioxide wash system 34 is well suited for implementation in aresin recycling method that produces essentially contaminant-freesynthetic resin material in an environmentally safe and economicalmanner. In general, the method includes receiving and sorting the resin.Once the resin has been sorted, it is ground into particles. Theparticles are then exposed to a solvent, the solvent contacting theresin particles and substantially removing contaminants on the resinparticles. After separating the particles and the resin, a solventremoving agent is used to remove any residual solvent remaining on theresin particles after separation. The substantially contamination-freeparticles are then sorted by type. In various embodiments, the resin isreceived in bales and initially sorted by color before grinding. Thesolvent is an organic solvent and the solvent removing agent is either aliquid or supercritical carbon. In the final sorting, thecontamination-free particles are separated by type, such as HDPE, PET,PVC, etc.

Referring to FIG. 3, a diagram illustrating a resin recycling method andapparatus according to the present invention is shown. The recyclingsystem 300 includes one or more bale breakers 302, one or more trommels304, one or more sorters 306, one or more grinders 308, one or more airclassifiers 310, one or more silos 312, the multi-tank solvent washsystem 10, hydro cyclone 112, spin dryer 120, silo 30, loader 314, oneor more carbon dioxide wash systems (34 a, 34 b, and 34 c), an airaspirator 316, silo 318, an optical sorter 320, infrared sorter 321, anda pelletizer 322.

It should be noted that for the sake of simplicity, only one recyclingline including solvent wash system 10, hydro cyclone 112, spin dryer120, silo 30, loader 314, one or more carbon dioxide wash systems (34 a,34 b, and 34 c), an air aspirator 316, silo 318, an optical sorter 320,and infrared sorter 321 is shown in the figure only for clear plasticresin. In an actual implementation of the present invention, either thenon-clear (i.e., green) resin would be separated. When a sufficientamount of the non-clear resin was collected, it would be run through theresin recycling method and apparatus as shown in FIG. 3. Alternatively,a parallel recycling line including multi-tank solvent wash system 10,hydro cyclone 112, spin dryer 120, silo 30, loader 314, one or morecarbon dioxide wash systems (34 a, 34 b, and 34 c), an air aspirator316, silo 318, an optical sorter 320, infrared sorter 321, and apelletizer 322 would be provided for the sorted green plastic resin.

It should be noted that the number of tanks in the solvent wash systemand the number of carbon dioxide systems 34 is arbitrary and is selectedbased on the desired throughput of the system. The numbers of tanks andcarbon dioxide systems illustrated and described herein should in no waybe construed as limiting the invention. Either more or fewer solventwash tanks and carbon dioxide systems may be used.

The bale breaker 302 is designed to remove the retaining wires or cablesbinding bales of compressed containers. As the bales are received, thebale breaker removes the wires holding the bale together and thenforwards the bale to the trommel 304. In the trommel 304, the compressedcontainers are repeatedly lifted, rotated and dropped in a tumblingaction, causing the individual containers to separate upon impact. Debrisuch as bottle caps and dirt are loosened by the tumbling action andtypically fall to the wayside. As the containers are tumbled in thetrommel 304, they eventually separate and are forwarded onto a conveyorbelt (not shown) and are then fed to the optical sorters 306. In oneembodiment, the optical sorter 306 separates the individual containersby color. In the example shown, into a clear stream and a green stream.The containers of the two streams are then fed into two grinders 308respectively. Each grinder 308 is designed to reduce the containers intoapproximately ⅜ inch flake shaped resin particles of like color. Thegrinders 308 are heavy duty industrial type that include a large numberof blades that grind the containers into the particles in a grindingchamber. Silos 312 are used to store the clear and green resin particlesrespectively.

The resin particles are next introduced into multi-tank solvent washsystem 10 from the silo 312. As described in detail above, the particlesare exposed to a solvent in the tanks, thereby substantially removingcontaminants on the particles. The hydro cyclone 112 separates the solidwaste material present in the slurry exiting the solvent wash system 10and the spin dryer 120 is used to separate the solvent from the resinparticles. The particles are then stored in another silo 30 before beingloaded by loader 314 into the carbon dioxide wash systems 34 a, 34 b,and 34 c. The air aspirator 316 separates any bits of label paper orother light material present on the substantially solvent-free resinexisting the carbon dioxide wash. The optical sorter 320 is used toseparate the resin stored in silo 318 by type, for example HDPE, PET,PVC, mixed plastic, vinyl chloride, polyethylense, etc. Infrared sorter321 sorts by color. In an optional step, the sorted resin particles maybe pelletized by pelletizer 322. Once the particles have been sorted bytype and optionally pelletized, the material can be recycled and reusedto make packaging containers and bottles.

With the above describe system and method, the sorting of the plasticresin is purposely done at different stages of the process. Thisredundancy helps assure that the final product is sorted by resin typeand color to a very high degree of accuracy. As a general rule of thumb,the bales as received are typically “pre-sorted” That is, the balesgenerally contain one type of plastic resin, such as either PET or HDPE.The problem with the bales, however, is that containers in the bales aretypically pre-sorted by humans. The bales consequently often containcontainers of a resin type that does not belong in the bale due to humanerror. The optical sorter 306 performs a first sorting by color. Theresin sorted by color then travels through separate solvent wash andcarbon dioxide wash lines as described above. Sorting is also performedwithin the multi-tank solvent wash system 10. As noted above, byselecting the specific gravity of the solvent, high density resin can besorted or separated from low density materials. For example, manysynthetic resin material containers made from polyethylene terephthalate(PET) employ caps made from less dense polypropylene material. It isoften desirable to separate these two kinds of materials duringrecycling operations. The less dense polypropylene material may beskimmed from the top of the solvent tanks and collected. When asufficient amount of the polypropylene material is collected, it too maybe passed through the system shown in FIG. 3. Sorting is also performedat the back end of the system and method. The optical sorter 320 sortsby the type of resin, such as HDPE, PET, PVC, mixed plastic, vinylchloride, polyethylense, etc. An optional sorter 321 also sorts bycolor. By building sorting redundancy into the system, the final productcan be sorted to a very high degree of accuracy.

The aforementioned system is also designed to remove any paper labelsand similar contaminants provided on the bottles and containers receivedon the bales. Paper labels are typically attached to bottles andcontainers by glue on the edges of the label. During grinding in thegrinders 308, the non-glued portion of the labels on the containers aretypically liberated. The ground resin particles are next passed throughair classifiers 310. Using an adjustable airflow and baffles, theclassifiers 310 blow or remove fines and light fragments, such as theliberated labels, from the resin particles. In the multi-tank solventwash system 10, the glue used to attach labels onto the resin particlesis typically dissolved and remove, liberating any remaining portion ofthe labels affixed to the resin by the glue. Finally, the air aspirator316 removes any remaining bits and pieces of labels, other fines orlight fragments not removed by either hydrocyclone 112 or the spin dryer120. As a result, labels or other fines are substantially removed fromthe resin particles stored in silo 320.

The solvent recycle station 26 includes, in one embodiment, a dirtysolvent tank 330, a solvent still 322 and a clean solvent tank 334.During recycling operations, the solvent in the multi-tank system 10becomes dirty from the contaminants removed from the resin particles.When the solvent needs to be replaced, it is removed from the multi-tanksolvent wash system 10 and stored in the dirty solvent tank 330. Cleansolvent is then removed from the clean solvent tank 334 to replenish theremoved solvent from the tanks. The dirty solvent is pumped into solventstill 332 while pulling a vacuum at a very high temperature (e.g. 250 to350 degrees F., and in one specific embodiment 300 degrees F.), causingthe dirty solvent to convert into a gaseous state. The contaminants,however, remain in the solid state and drop into a collect bucket in thesolvent still. The cleaned solvent is then cooled back to the liquidstate in coils and then stored in the clean solvent tank 334 for lateruse.

The pellitizer 322 is a machine that converts the cleaned resinparticles, typically in flake form, into pellets. The pellitizer heatsthe resin particles from a solid state into a liquid state. The liquidis then pushed or extruded through a filter screen and die plate. Thefilter screen removes any particles or contaminants in the liquid resin.As the liquid is extruded through the die plate, knife blades cut theresin, forming pellets upon solidification.

In the beverage industry for example, the bottles are often made fromvirgin PET material in pellet form. With the present invention, therecycled resin in pellet form is sufficiently clean and free ofcontaminants, residue, or odors that it can readily meet or exceed thehigh qualification standards required by most bottlers. Thus with thesystem and system for the present invention, the bottles can be made forthe soda and beverage industry using completely recycled resin, or a mixof recycled and virgin resin.

Although the invention has been described with reference to theembodiments illustrated in the attached drawing figures, it is notedthat equivalents may be employed and substitutions made herein withoutdeparting from the scope of the invention as recited in the claims. Forexample, the sorting can occur using some other criteria besides thecolor or the containers or the type of material. The size in which theresin particles are ground is also optional and can be made eitherlarger or smaller than specified herein. The type of solvent or thesolvent removing agent used is also arbitrary and does not necessarilyhave to be of the same type or phase described herein. Having thusdescribed the various embodiment of the invention, what is claimed asnew and desired to be protected by Letters Patent includes thefollowing:

1. An apparatus, comprising: a solvent wash vessel to expose resinparticles to a solvent, the solvent contacting the resin particles inthe wash vessel to substantially remove contaminants on the resinparticles; a separator to separate the solvent from the resin particlesafter removal from the solvent wash vessel; and a closed loop carbondioxide system configured to expose the resin particles to carbondioxide to substantially remove any residual solvent remaining on theresin particles after separation, the closed loop carbon dioxide systemfurther comprising: a carbon dioxide vessel to exposed the resinparticles to carbon dioxide, the carbon dioxide substantially removingthe solvent remaining on the resin particles and becoming laden withsolvent in the carbon dioxide vessel; and a separation vessel configuredto separate the solvent from the solvent laden carbon dioxide so thatthe solvent and the carbon dioxide can be reused.
 2. The apparatus ofclaim 1, wherein the pressure of the carbon dioxide in the carbondioxide vessel is maintained in a range of one of the following:approximately 650 to 1000 pounds per square inch; or approximately 700to 800 pounds per square inch.
 3. The apparatus of claim 1, wherein thetemperature of the carbon dioxide in the carbon dioxide vessel ismaintained in one of the following temperature ranges: approximately 20to 100 degrees Celsius; approximately 30 to 90 degrees Celsius;approximately 60 to 70 degrees Celsius;
 4. The apparatus of claim 1,wherein the carbon dioxide in the carbon dioxide vessel is maintained inone of the following states: liquid carbon dioxide; or supercriticalcarbon dioxide.
 5. The apparatus of claim 1, wherein the carbon dioxidevessel further comprises: a first opening configured to receive carbondioxide; and a second opening configured to allow carbon dioxide ladenwith solvent to exit the carbon dioxide vessel, wherein, between thefirst opening and the second opening, the carbon dioxide flows adjacentthe resin particles in the carbon dioxide vessel, dissolves the solventon the resin particles, and carries the solvent away from the resinparticles in the carbon dioxide exiting the second opening.
 6. Theapparatus of claim 1, further comprising a heat exchanger coupledbetween the carbon dioxide vessel and the separation vessel, the heatexchanger being configured to cool the solvent laden carbon dioxideexiting the carbon dioxide vessel.
 7. The apparatus of claim 1, furthercomprising an expansion device coupled between the carbon dioxide vesseland the separation vessel, the expansion device being configured tocontrol the pressure of the carbon dioxide so that the carbon dioxideladen with the solvent is in a gaseous phase when entering theseparation vessel.
 8. The apparatus of claim 1, wherein the solventladen carbon dioxide is maintained at a predetermined temperature andpressure in the separation vessel such that the carbon dioxide has anegligible solubility for the solvent so that the solvent substantiallyprecipitates out of the carbon dioxide.
 9. The apparatus of claim 1,further comprising a reservoir configured for storing carbon dioxidefrom the separation vessel and providing the carbon dioxide to thecarbon dioxide vessel.
 10. The apparatus of claim 9, further comprisinga compressor and a heat exchanger coupled between the reservoir and thecarbon dioxide vessel to control the pressure and the temperature topredetermined levels for the carbon dioxide entering the carbon dioxidevessel from the reservoir.
 11. The apparatus of claim 1, wherein thesolvent is an organic solvent having properties configured to solvateone or more of the following types of contaminants from the resinparticles: oil; milk, soda; pesticides; detergents; or a combinationthereof.
 12. The apparatus of claim 1 wherein the solvent is selectedfrom the group consisting of amyl propionate, butyl butyrate, alkyllactates, ethyl hexyl acetate, dibasic esters, methyl soyate, ethylsoyate, cyclohexanone, methyl ethyl ketone, dipropylene glycol,dipropylene glycol methyl ether, trichloroethylene, xylene, ethanol,tetrahydrofurluryl, hexane, mineral spirits, monoethanolamine,d-limonene, dimethyl formamide, n-methyl pyrrolodine, propylenecarbonate, and combinations thereof, and ‘wherein said alkyl lactate isselected from the group consisting of methyl lactate, ethyl lactate,isopropyl lactate, butyl lactate and combinations thereof.
 13. Theapparatus of claim 1, wherein the solvent is an alkyl ester solventhaving the general formula RCOOR′, wherein R and R′ are independentlyselected from C1-C10 alkyl groups and R contains at least one hydroxylgroup.
 14. The apparatus of claim 1, wherein the resin particles areselected from the group consisting of polypropylene, polyethylene,polyethylene terephthalate, nylon, teflon, polytetrafluoroethylene,polyvinylidene fluoride, and combinations thereof.
 15. The apparatus ofclaim 1, wherein the separator comprises a spinning machine tosubstantially separate the solvent from the resin particles.
 16. Amethod, comprising: exposing resin particles to a solvent, the solventcontacting the resin particles in a wash vessel to substantially removecontaminants on the resin particles; substantially separating thesolvent from the resin particles after removal from the solvent washvessel; exposing the resin particles to carbon dioxide in a carbondioxide vessel to substantially remove any residual solvent remaining onthe resin particles after separation, the carbon dioxide becoming ladenwith solvent in the carbon dioxide vessel; and separating the solventfrom the solvent laden carbon dioxide in a separation vessel so that thesolvent and the carbon dioxide can be reused.
 17. The method of claim16, further comprising controlling the pressure of the carbon dioxide inthe carbon dioxide vessel in a range of one of the following:approximately 650 to 1000 pounds per square inch; or approximately 700to 800 pounds per square inch.
 18. The method of claim 16, furthercomprising maintaining the temperature of the carbon dioxide in thecarbon dioxide vessel in one of the following temperature ranges:approximately 20 to 100 degrees Celsius; approximately 30 to 90 degreesCelsius; approximately 60 to 70 degrees Celsius;
 19. The method of claim18, further comprising maintaining the carbon dioxide in the carbondioxide vessel in one of the following states: liquid carbon dioxide; orsupercritical carbon dioxide.
 20. The method of claim 16, whereinexposing the resin particles to carbon dioxide in the carbon dioxidevessel further comprises: introducing carbon dioxide into the carbondioxide vessel through a first opening; exposing the resin particles tothe carbon dioxide in the carbon dioxide vessel; dissolving the solventon the resin particles as the resin particles are exposed to the carbondioxide so that the carbon dioxide becomes laden with the solvent; andcausing the carbon dioxide laden with the solvent to exit the carbondioxide vessel through a second opening in the carbon dioxide vessel.21. The method of claim 16, further comprising cooling the solvent ladencarbon dioxide exiting the carbon dioxide vessel.
 22. The method ofclaim 16, further comprising controlling the pressure of the carbondioxide so that the carbon dioxide laden with the solvent is in agaseous phase when entering the separation vessel.
 23. The method ofclaim 16, further comprising maintaining the solvent laden carbondioxide at a predetermined temperature and pressure in the separationvessel so that the carbon dioxide has a negligible solubility for thesolvent, causing the solvent to substantially precipitate out of thecarbon dioxide.
 24. The method of claim 23, further comprising storingthe carbon dioxide in a reservoir after the removal of the solvent fromthe carbon dioxide in the separation vessel.
 25. The method of claim 24,further comprising controlling the pressure and the temperature of thecarbon dioxide to predetermined pressure and temperature levels when thecarbon dioxide is introduced into the carbon dioxide vessel from thereservoir.
 26. The method of claim 16, wherein the solvent is an organicsolvent having properties configured to solvate one or more of thefollowing types of contaminants from the resin particles: oil; milk,soda; pesticides; detergents; or a combination thereof.
 27. The methodof claim 16 wherein the solvent is selected from the group consisting ofamyl propionate, butyl butyrate, alkyl lactates, ethyl hexyl acetate,dibasic esters, methyl soyate, ethyl soyate, cyclohexanone, methyl ethylketone, dipropylene glycol, dipropylene glycol methyl ether,trichloroethylene, xylene, ethanol, tetrahydrofurluryl, hexane, mineralspirits, monoethanolamine, d-limonene, dimethyl formamide, n-methylpyrrolodine, propylene carbonate, and combinations thereof, and whereinsaid alkyl lactate is selected from the group consisting of methyllactate, ethyl lactate, isopropyl lactate, butyl lactate andcombinations thereof.
 28. The method of claim 16, wherein the solvent isan alkyl ester solvent having the general formula RCOOR′, wherein R andR′ are independently selected from C1-C10 alkyl groups and R contains atleast one hydroxyl group.
 29. The method of claim 16, wherein the resinparticles are selected from the group consisting of polypropylene,polyethylene, polyethylene terephthalate, nylon, teflon,polytetrafluoroethylene, polyvinylidene fluoride, and combinationsthereof.